1. Field of the Invention
The present invention relates to a wire dot printer head and a wire dot printer.
2. Discussion of the Background
The wire dot printer head is a device which, when the armature is rocked to a printing position by rocking an armature obtained by connecting printing wires between the printing position and a standby position, performs printing by causing a tip portion of the wire to collide with a printing medium such as a sheet.
Among such wire dot printer heads, there has been proposed a device which performs printing by generating magnetic flux around the armature targeted for rocking by coils to thereby form a magnetic circuit for attracting the armature from the standby position to the printing position (See Japanese Patent Laid-Open No.4-105945). In a wire dot printer head of Patent Literature 1, the armature has a support shaft, and is provided in such a manner as to be freely pivotable with the support shaft as a center. Between the support shaft of the armature and a by-pass magnetic path provided on a yoke, for forming a magnetic circuit, there has been provided a sheet-shaped spacer formed of SK material. Thereby, the support shaft of the armature is prevented from wearing the surface of the by-pass magnetic path during a printing operation.
When, however, between the support shaft of the armature and the by-pass magnetic path, there is provided a spacer made of SK material as described in the Patent Literature 1, a magnetic characteristic in the magnetic circuit is deteriorated because the magnetic permeability of the spacer is lower than that of the by-pass magnetic path or the yoke. For this reason, any stable rocking operation of the armature cannot be realized, and in addition, the magnetic characteristic required for high-speed printing is not acquired. Consequently, high-speed printing cannot be performed. Particularly, as the printing speed in recent years becomes faster, it is required that the armature be rocked, for example, 2500 numbers of times/second between the printing position and the standby position. Therefore, deteriorated magnetic characteristic has become an important issue.